Abstract The mineraological characters of the rocks to which this memoir relates have been so fully described by Maccullouch and other writers, that it is not necessary to enter into any details on that head; my object is to describe the unusual arrangement of the layers of foliation which have given an appearance of stratification to Gneiss and Mica Schist, to show the relation of their foliation to the cleavage of the stratified slates, and to sketch out roughly the direction of the foliation and cleavage through the North of Scotland. The most important remarks yet published upon these subjects will be found in the sixth chapter of Mr. Darwin’s “Geological Observations on South America,” which, in addition to his own views and observations, contains a summary of what had then been done by others: Mr. Darwin’s remarks will be frequently quoted in this paper. I must also refer the reader to two papers on Slaty Cleavage, which I laid before the Geological Society in 1846 and 1848, and which are published in the third and fifth volumes of that Society’s Journal.